The present invention relates generally to methods and apparatus for perforating a well, and more specifically relates to collapsible perforating assemblies for use in perforating a well.
After a well is drilled and the casing is set, the well is often perforated through use of tubing conveyed perforating equipment. In a tubing conveyed perforating operation, the perforating guns are carried on the tubing string, and are typically actuated either by dropping detonating bars down the tubing, or by applying hydraulic pressure proximate the gun firing head, to actuate the firing head. In order to produce the well after perforation, it is often desirable to drop the gun assembly into the wellbore. The gun assembly is dropped off into the "rat hole," i.e., that area of the wellbore below the production zone.
In many cases multiple perforating guns will be utilized in a perforating assembly with the perforating guns spaced at desired intervals. The spacing of the perforating guns allows the guns to be utilized to perforate different zones on a single trip, to perforate different horizons of a single zone, or to avoid perforating a weak section of casing. Such perforating assemblies with spaced guns may extend a considerable length, for example thirty to sixty feet, or longer. Where the guns are to be dropped from the tubing after detonation, the rat hole must be able to accommodate this length. If the rat hole does not extend far enough below the production zone, conventional perforating assemblies may not be able to be dropped off.
Accordingly, the present invention provides a new perforating assembly which is adapted to space perforating guns a desired distance apart prior to their detonation, and to be telescopically collapsed after gun actuation so that when dropped off, a relatively short rat hole will be able to accommodate the gun assembly. Accordingly this collapsible perforating assembly facilitates the use of long, spaced, intervals of tubing conveyed perforating guns, and the dropping of the assembly, even when the well rat hole is shorter the original length of the perforating assembly.